This invention relates to an electronic musical instrument capable of producing special performance effects such for instance as an automatic arpeggio performance. Known in the art of electronic musical instruments is one in which a predetermined number of tone production channels are provided, data as to depressed keys are assigned to respective tone production channels by digital technique, and plural tones are produced simultaneously through these tone production channels. In this type of electronic musical instrument, arrangements are made for preventing assignment of one and the same tone to plural tone production channels. An electronic musical instrument of this type, which is modified to carry out special performances such as an automatic arpeggio performance and an automatic bass performance is described in the U.S. Pat. No. 4,158,978 entitled "Electronic musical instrument" or in the U.S. Pat. application Ser. No. 825,443, now U.S. Pat. No. 4,184,401, entitled "Electronic musical instrument with automatic bass chord performance device" both assigned to the same assignee as the present case. The former patent relates to an electronic musical instrument adapted to perform a kind of automatic arpeggio performance. In this instrument, one or more tones are produced one after another with a predetermined time interval by assigning tone production for one or more keys depressed in the keyboard separately to one or more tone production channels and thereafter controlling timing of tone production in the respective channels. Accordingly, tone production of depressed keys is not always made in the tone production channels to which tone production of the keys depressed for the automatic arpeggio performance has been assigned, but tone production is made in only one channel selected in accordance with the tone production timing control, and this tone production channel in which tone production is actually made is switched from one channel to another. Since the number of the tone production channels is limited (e.g. 12), if the number of the keys depressed for the automatic performances increases, the number of the channels which are available for an ordinary tone production decreases, which is a disadvantage of this type of instrument.
The latter application mentioned above relates to an instrument capable of conducting an automatic bass performance in which data of a key depressed in the keyboard is modified by a calculating operation before the key data is assigned to a tone production channel and a tone corresponding to the modified key data is assigned to a tone production channel. According to this type of instrument, however, a tone corresponding exactly to the depressed key cannot be produced with a result that a free performance in the electronic musical instrument is hampered.
It has been a general tendency in the automatic arpeggio performance conducted by prior art electronic musical instruments including the above described instruments to selectively control timing of production of tones for depressed keys so that production of tones corresponding exactly to the depressed keys is cancelled when the automatic performance is being made. Further, it is common in the prior art instruments to designate a tone constituting a basic tone for the automatic performance directly from the keyboard. In this case, the keyboard does not perform its proper function of manual key selection means for a manual operator any longer but serves merely as an auxiliary means for an automatic performance (e.g. means for designating a root note or a chord or means for designating arpeggio constituting tones).
In prior art electronic musical instruments before the above described United States patent applications, it was customary to conduct the automatic performance by an independent automatic performance device which is merely added to a manual tone generation device coupled to a keyboard. According to this type of prior art instrument, a function of producing tones corresponding directly to depressed keys and a function of producing tones for the automatic performance can coexist without sacrificing either one of them. This type of instrument, however, tends to become bulky and expensive and it will be apparently more advantageous in respect of circuit construction and performance functions if circuitries for performing both functions are associated with each other. The instruments described in the above mentioned two United States patent applications has the circuitries for both functions associated with each other but still have the above described disadvantages.